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The World Health Organization yesterday placed cellphones on its list of items that can potentially cause cancer in humans, based on studies suggesting there might be a small increased risk of glioma, a rare brain cancer, from heavy use of the mobile device.

The group said the evidence of harm from cellphones is limited and is based on inconclusive research, but warrants classification of the phones as “possibly carcinogenic to humans’’ — a category that includes 266 items, from gasoline exhaust to dry cleaning agents to talcum powder. WHO officials suggested that consumers take precautions to keep their mobile phone antenna away from their head by using hands-free devices or the speaker phone feature, or texting when possible.

“The evidence, while still accumulating, is strong enough to support a conclusion . . . that there could be some risk, and therefore we need to keep a close watch for a link between cellphones and cancer risk,’’ said Dr. Jonathan Samet, a University of Southern California epidemiologist who chaired a panel of 31 international scientists charged with reviewing the research on the risks from the phones’ electromagnetic fields.

The findings were released at the end of an eight-day meeting in Lyon, France, organized by the WHO’s International Agency for Research on Cancer. The agency’s director emphasized in a statement that more long-term research is needed to understand the risks of cellphone use. Meanwhile, said director Christopher Wild, “It is important to take pragmatic measures to reduce exposure.’’

Cancer specialists not involved in the review urged cellphone users not to be alarmed by the new classification, because the research has not yet shown that the devices cause harm, but at the same time they said it’s reasonable to take steps to protect against unknown risks.

“I follow this literature pretty closely and am asked about it almost daily — by patients who already have brain tumors,’’ said Dr. William Curry Jr., a neurosurgeon at Massachusetts General Hospital. “To date, I would have said there is not convincing evidence that cellphone-associated radiation causes brain tumors, either benign or malignant. But I would say there’s not convincing evidence, either, that it doesn’t.’’

Curry said he generally tries to use his cellphone in speaker mode or to send text messages because of the emerging evidence that cellphones can alter brain physiology. Still, he noted, it is not yet known whether those changes are a risk factor for cancer or not. Studies of cancer risk and cellphone use have also been flawed because of the ways in which they are conducted, he said; for example, some rely on people’s recollections about cellphone usage years earlier, and people with brain tumors may be more inclined to report greater cellphone use in the past than people without cancer.

The cellphone industry issued a statement yesterday saying the WHO action “does not mean cellphones cause cancer.’’ In the past, said John Walls, vice president of public affairs for CTIA-The Wireless Association, the International Agency for Research on Cancer “has given the same score to, for example, pickled vegetables and coffee.’’

The cancer agency said its cellphone review panel considered hundreds of scientific articles, as well as unpublished research. In particular, it cited a large international study published last year that overall found no increased risk of two types of brain cancer with cellphone use. But among the heaviest cellphone users, the study, published in the International Journal of Epidemiology, found a 40 percent increased risk of the rare glioma tumor. Even the researchers considered the finding inconclusive, however.

“Personally, I’m not convinced that there’s a risk,’’ said Dr. Dimitrios Trichopoulos, a professor of cancer prevention at the Harvard School of Public Health, who was not involved in the study. “But even if the risk is true, it’s still pretty small.’’

On the other hand, it’s tough to prove that something is safe. One intriguing study published in the February issue of the Journal of the American Medical Association found that cellphones lead to a temporary change in the brain’s metabolism of sugar — which suggests that their use does have an impact on brain function, though not necessarily a harmful one.

Still, that was enough to get study author Dr. Nora Volkow, director of the National Institute for Drug Abuse, to limit her cellphone use; she said earlier this year that she uses her cell only on speaker or with wired earpieces to keep the antenna farther away from her brain.

Cellphone users interviewed on Boston Common had mostly mild reactions to the news, with many asserting that they’re not worried enough to change their cellphone habits. Ronnie Foster, 41, said he’s waiting for definitive proof before taking his phone off his ear, calling it “my only lifeline to my family,’’ while Eddie Mello, 30, says he’s waiting for the “surgeon’s general warning on the box’’ before he will limit his talk time.

But Dave Hanley, 27, of Brighton said he thinks cellphones are going to become as big an issue as cigarette smoking. “Cellphones haven’t been around long enough for people to take [them] seriously,’’ he said.

Cellphone users may have more questions than answers. “We have to consider the possibility that cellphones could have an effect on the brain, and those effects may not all be positive,’’ said Dr. Mark Johnson, a neurosurgeon at Brigham and Women’s Hospital. While Johnson said he was not too worried about his own cellphone use, he is considering buying a hands-free device so he can minimize his exposure. And he is also going to urge his children to speak on the phone less — while noting that their exposure is already pretty limited since they tend to text.